Field of the Invention
Embodiments of the invention generally relate to the field of display technologies, and specifically, to a thin-film transistor having a channel structure having an increased width-length ratio and a manufacturing method thereof, a display substrate and a display device.
Description of the Related Art
With continuous development of liquid crystal display technologies, thin-film transistors (TFTs) are widely used in display devices, such as TFT LCDs (liquid crystal displays). In a TFT LCD, luminance of a subpixel is adjusted through controlling a voltage on each of subpixels arranged in an array, and thereby a complete and accurate display image is achieved. When a turn-on voltage Von is applied to gate electrodes in a certain row in the array so that the TFT device is turned on, a source and a drain located at both sides of a TFT channel are communicated with each other, and a given signal is applied on a subpixel electrode through a data line. A voltage difference between the subpixel electrode and a common electrode determines a deflection state of liquid crystal molecules in region of this subpixel, and finally, affects luminance and display performance of the subpixel.
Improvement of quality of display image of a LCD has become one focus of competition among LCD products. A value of the turn-on voltage directly determines the quality of the display image, such that an important aspect of research is to increase an on-current Ion of the TFT. Aperture ratio is also an important factor among factors that affect the luminance of the display image. Aperture ratio is a ratio between an area of a light transmitting region of a subpixel except wires, transistors and the like thereof (for example, hidden by a black matrix) and an entire area of the subpixel. The higher the aperture ratio, the higher a light transmitting efficiency is. When light is emitted from a backlight unit, not all the light can pass through the panel. For example, the light may be blocked by signal wires for source driver chip and gate driver chip of the LCD, the TFT itself, a region where a storage capacitor for storage voltage is located, or the like. Besides of these regions being not entirely transparent, light passing through these regions cannot be controlled by a voltage such that these regions cannot display a proper gray level. Thus, all these regions should be shielded by a black matrix to prevent them from interfering with other light transmitting regions. A ratio between an effective light transmitting region and the entire area of the panel is called as the aperture ratio. Therefore, the quality of the display image can be significantly improved through reducing the size of the TFT, increasing on-current of the TFT, or the like.
Another important factor that affects the on-current of a thin-film transistor is a width-length ratio (W/L) of the transistor. FIGS. 1 and 2 schematically show a structure of a thin-film transistor. As shown in the figures, the thin-film transistor comprises a gate 11, a gate insulation layer 12 and an active layer 13 stacked on a substrate 10, the active layer 13 may also be covered with a passivation layer 14. The active layer 13 is formed therein with a source (S) region, a drain (D) region, and a channel region between the source region and the drain region. In the thin-film transistor shown in FIGS. 1 and 2, the channel structure thereof is a planar structure, that is, a surface of the active layer facing toward the gate is flat or substantially flat at least in the channel region. Thus, a length L and a width W of the channel region of such thin-film transistor are defined by the source region and the drain region, and are generally limited by manufacturing processes, such as a minimum size of photoetching process. Usually, reducing the minimum size of photoetching process to reduce the length L and in turn increase the width-length ratio W/L of the channel region is difficult.